1. Field of the Invention
The invention relates to a coating process. More particularly, the invention relates to a method of applying a metallic coating by decomposing a metallic compound. Most particularly the invention relates to a method of applying a diffusion coating by applying a metallic compound and a halide activator. The invention also relates to a cerium coated nickel-base or iron-base alloy article.
2. Discussion of the Related Art
Chemical vapor deposition is known for use in coating a metal substrate. Pack cementation process is one technique for carrying out chemical vapor deposition. In general, a coating powder is applied to the substrate to form the cementation pack. The coating powder comprises a coating metal oxide powder, halide salt and optionally powder filler. The cementation pack is heated under inert or reducing atmosphere to an effective temperature to form a diffusion coating. At the effective temperature the halide salt reacts with the metal powder to form metal halide vapors. The metal halide vapors diffuse into the substrate. The metal halide decomposes on contact with the metal substrate, to form the solid state diffusion coating.
There remains in the art an unfulfilled need for a process to form a diffusion coating of cerium on a metal surface.